Fixed spelling and grammatical errors

[rbrasga]

Not sure if this is worth the effort, but I fixed a lot of typos.

I manually reviewed each line change for accuracy.

[ivyl]

openvr and steamworks headers are direct source imports from other projects,see: https://github.com/ValveSoftware/openvr/ and: https://partner.steamgames.com/doc/sdk.

Since those are external imports we want to keep them as close to originals, even if that means typos.

As of other changes, like the ones to the .md those are welcome. If you can trim the YPR to only contain those I can merge it.